It is known that rapidly initiated reactions of this type may be carried out in a mixer-reactor consisting of a substantially rotationally symmetrical casing. The casing contains a substantially rotationally symmetrical mixing chamber having separate inlets for at least two substances and an outlet. The inlet for the at least first substance is provided within the axis of the mixing chamber and the inlet for the at least second substance is constructed in the form of a plurality of nozzles arranged rotationally symmetrically to the axis of the mixing chamber; see, for example, U.S. Pat. Nos. 4,851,571, 4,915,509 and 5,117,048.
The quality of the products prepared in apparatus of this type depends very greatly on the quality and rate of mixing of the fluid substances. Here, the injection of even flows of material through each of the nozzles into the mixing chamber is of crucial importance.
A disadvantage of the known mixer-reactors is that, in the course of time, caking and subsequent clogging occur inside the nozzles, resulting in the disturbance of the injection of equal flows of material through all the nozzles. Therefore, high demands with regard to freedom from solids and from reactive foreign substances have to be imposed, at least on the second substance. There is an increased risk of clogging, particularly where the second substance is dissolved or suspended in a solvent or in a suspending medium and the solvent or suspending medium is separated from the product and reused. To lower the tendency of caking and clogging, it is necessary to carry out an extensive purification process for the solvent or suspending medium to be reused, in order to lower the tendency to clogging. Caking may also occur on the nozzles on the entry side to the mixer as a result of secondary reactions with the first substance. Where caking and/or clogging occur, the continuous process has to be interrupted and the mixer-reactor taken apart and cleaned. This causes considerable idle periods. Where hazardous substances are used, as in the case of phosgene, industrial hygiene regulations necessitate expensive measures during the disassembly of the mixer-reactor, such as the thorough rinsing of the reactor before disassembly, protective clothing, exhaustion of the atmosphere, breathing apparatus, and etc.